1. Field of the Invention
The present invention relates to an onboard equipment network system including at least one detecting apparatus, such as a radar, a sonar or an echo sounder, and/or a positioning apparatus, such as a receiver for the Global Positioning System (GPS receiver), and a common display device, wherein image data obtained by the detecting apparatus and/or the positioning apparatus is transmitted through a network and displayed on the display device.
2. Description of the Background Art
Conventionally, it is necessary for such onboard equipment as a radar, a sonar, an echo sounder or a GPS receiver to uninterruptedly monitor situations surrounding a vehicle or target situations. Specifically, they need to continuously, or continually, receive incoming signals and produce detection data or positioning data. Accordingly, this kind of onboard equipment has to handle an enormous amount of received data, which is different from ordinary image data or command data, and for transmitting the received data to a display device for on-screen display, the provision of a data transmission line having a large transmission capacity is essential.
A detecting apparatus like a radar or a sonar converts received echo signals which are originally formatted for a polar coordinate system into signals for a Cartesian coordinate system and displays an image of received echoes on a raster-scan display. A graphical representation of the received echo signals reveals that these signals are densely arranged near the sweep origin and become progressively sparser outward as can be seen from FIG. 14, which represents the geometric arrangement of the received signals. Thus, when the received signals are converted into the signals formatted for the Cartesian coordinate system for raster scan, each pixel close to the sweep origin contains data derived from a larger number of echo signals than a pixel located away from the sweep origin. In other words, pixels close to the sweep origin correspond to large numbers of echo signals. Therefore, if the echo signals are to be handled in their original form, or in the polar coordinate system, an enormous amount of data would occur on the pixels close to the sweep origin. While each of the aforementioned detecting apparatus transmits data reformatted for the Cartesian coordinate system to their display device to solve the problem related to data transmission capacity, the amount of data is still considerably great compared to ordinary command data, for example, because the signals are received uninterruptedly.
To properly handle such enormous amounts of data without being adversely affected by external influences, a data transmission line having a large transmission capacity is employed to interconnect a core device of the aforementioned conventional detecting or positioning apparatus which receives detection signals or positioning signals and generates image data and a display device which displays the image data. In addition, the core device and the display device are positioned as close as possible to each other and they are normally enclosed in a single housing.
As a result of recent years' advances in communications technology, it has become possible to exchange data to and from individual apparatus through a communications network (e.g., local area network, or LAN) and selectively display desired data or simultaneously display the data of individual apparatus. It has also become possible to display the data or images on a monitor which is commercially available on the market.
It is however necessary for the aforementioned onboard equipment to uninterruptedly receive the detection or positioning signals, convert these signals into appropriate image data and display images on a display. Therefore, even if the received signals are reformatted into the signals for the Cartesian coordinate system as stated above and the resultant data are transmitted pixel by pixel, the amount of data to be transmitted from the core device of each apparatus is so enormous that it is often impossible to use a generally available communications network like the LAN for presentation on a common monitor due to limitations in the transmission capacity, for example.
In a case where the core device and the display device of each of the detecting and/or positioning apparatus are housed in a single housing, the individual detecting apparatus and/or positioning apparatus (e.g., GPS receiver) work as stand-alone systems, making it difficult to share their respective data. To make it possible to monitor and use the data of other apparatus, it is necessary to connect the individual apparatus by cables or other data transmission means, which requires additional expenses and installation space.
If the positioning data obtained by a GPS receiver is to be displayed on the display device of a radar, for example, there arises a problem that the display device of the GPS receiver becomes unnecessary.
Also, if the core devices of the individual detecting and/or positioning apparatus are simply connected to a network, there can arise a case where a common display device on the network is off while the individual core devices are on. In this case, it is impossible to display any data on the display device no matter whether the core devices are receiving and processing signals, resulting in a waste of electric power.